The overall objective of the proposed research is to gain insight into the mechanisms by which cariogenic bacteria such as Streptococcus mutans can synergistically and antagonistically interact with other bacteria during dental plaque formation. The specific objectives are: (1) to utilize our quantitative in vitro plaque forming assay to analyze factors involved in heterotypic interactions between oral bacteria. Bacteria which readily form plaque on human teeth such as Streptococcus sanguis and certain gram positive rods will be attached to glass vials modified to contain a stable covalently bound layer of polylysine. This initial layer of cells will be used as a base to analyze factors involved in heterotypic attachment of bacteria found in mature plaque. Emphasis will be placed on the conditions for cell preparation and cell surface components involved in adherence; 2. to analyze the interaction and association of the S. mutans dextransucrase with lipids in order to evaluate the role of such molecules in glucan production and sucrose-dependent adherence reactions. Emphasis will be placed on utilizing homogeneous enzyme preparations and phospholipids known to be produced by S. mutans and/or found in human saliva; and 3. to continue evaluation of the association between dextranase-producing oral bacteria and S. mutans. The ability of dextranase-producing bacteria to inhibit or enhance dextran-mediated heterotypic adherence by S. mutans will be evaluated. Plaque samples will be obtained from incipient white spot lesions and control sites on children's teeth and analyzed for the content of S. mutans and specific dextranase-producing bacteria. Emphasis will be placed on careful diagnosis of the sites to be sampled, the method for obtaining plaque and optimization of conditions for bacterial quantitation. The long-term goal is to define interactions involved in regulating the microbial content of plaqe which could be used to develop caries control measures based on selective inhibition of specific cariogenic bacteria.